Final answer:
The beans of the baobab tree were a staple in some desert regions, particularly in the Sahel, providing critical sustenance and other resources to local populations.
Step-by-step explanation:
The beans that became a staple food in some desert regions, particularly in the Sahel just south of the Sahara Desert, are from the baobab tree. The baobab tree, often referred to as the "tree of life," is renowned for its numerous uses, providing food, medicine, and shade to the inhabitants of the desert's border regions. Indigenous peoples in these areas, such as the nomadic Fulani, have relied on baobab beans for sustenance. Additionally, in the American Southwest, Ancestral Puebloans cultivated beans along with corn and squash at Mesa Verde, relying on these as their primary agricultural products. The inclusion of beans in their diet complemented the nutritional value of maize, which lacks the amino acid lysine, and helped to maintain soil nitrogen levels, thus preserving soil fertility over long periods.